Diffraction-grating replica.



No. 818,966. PATENTED APR. 24, 1906. P. RIVES. DIFPRACTION I(J'fRATIlH-rREPLICA.

APPLICATION FILED SBPT.29. 1905.

I l f f between the surface of tlie grating-replica -To alt floh/om; itmay conce-rn.-

STATES PATENT LoEEioE;

FREDERIC. NES, or WooponrrrE-onrHE-HUDSON, NEW JERSEY.

No. classe;

speciadation of Letters Patent.

DFFFiAcTioN-GRATINQREPLICA..

' :Patented April 2a, 190e.

ippiimitnsiai seemtrzaisoe'; seraiiiaasaess.

Be itknown that i, FnEbEmc E. Ives, a

citizen of the United States, residing' at'Woodcliife-on-the-Hudson,lVeehawken post-f iilice-,

New Jersey, have invented certain Improvements in Diffraction GratmgReplicas, of

. which thcfollowing is a specification. The object of my invention isito make a ing replica.

'I producing replicas of a diffraction-gratin consisted in properly'leveling thelorigina .25

replica of a diiraction-grating which will be ofbetter optical finalitythan those produced by the methods objectl attain in the mannerhereinafter set forth, reference being had tothe accompanyin drawings,in which-'- igure 1 is av sectional view, on an enlarged scale,illustrating the lirststa e of my im-` proved process of making a diractionfgrat- Figx2 isa similar view illustratprocess, and Fig. 3

ing the Asecondstaoe of the e completed repis a similar view-showing tHeretofore the most successful method of orrating and pouring upon itasolution o celluloid in. amyl acetate or similar solvent,

' permitting the film thus formed' to dry, and then placing the gratiwith its supe osed film, in-watei-,until the m loosened yan thenremoving the film and laying it, under water, upon a piece of plane g assurface outward, the lilm being then permitted Lto dry in contact withthe glass. method is subject, among others, to the followingobjectionsz-irst, irregularities in the thickness of the ilm distort theplane of the diiractin -surface, and although this distortion may e veryslight it isoptically of considerable importance; second, the thincelluloid film is very tender and elastic and probably always distortsin handling or shrinks unevenly in drying sufficiently to injure thedefiniti'bn `of thespectra; third, the delicate surface of the cast isexposed to injury, or; coveredwith a protecting-glass, reflections andthe cover-glass impair the performance of the grating in thespectrosco'pe. Incarrying out my invention I substitute a harder and esselastic material for the celluloid, dry out thesolvent more thoroughlythan is necessary when the cast is placed upon 'a glass latewith-its.face outward, place the cast ace downward on the plane lass,andseal the cast under another plane g ass by the use of a ,material orcompound having approxieretofore practiced. This s, with the ruled.

This

mately the same refractive index as the iilmcast.

For an original from whichto make the replica I prefer a Rowland metal.This is leveled lface up--as shown,

rating on .speculum for instance, at a in Figi. land Asaidfaoe is' t'ilm is'then pulled from the grating by forceps and drawn over the glassplate, which is then -lifted out'of the water,zwith the filmcast restingupon it with its incised side down. i

By means of gentle pressure with a photographic-print roller or othersuitable `implement the cast is then brought into uniform contact withthe glass plate and is' then covered With a 'pa'd of absorbent paper orother suitable niateriald, Fig. 2, upon which is laid.

anither plane glass e and a suitabl'ejveight,

for the purpose of permitting lthe film to dryv under pressure.

1 The drawings'are merely diagrammatic,

n'otrepresenting the relatiye thickness of the elements.

After removing the wet absorbent pad the film is exposed to air orgentlyheated to drive 'off4 the last traces o moisture, after which it isready for sealing up with the ooverlass.

Spirits of turpentine has a lower refractive index than the film-cast,and Canada balsem has a higher refractive index.` Dry Canada balsam may,therefore, bedissolved in vspirits of turpentine in such relative proortio'ns as.

to .produce a sealing compound aving almos't exactly thesamerefractiveindex as the film-cast, or boiled linseed-oil may`besubstituted for the spirits of turpentine and liquid Canada bal'sam fordry Canada balsam. A proper quantity of this solution is poured over theback of the film-cast, the coverglass g is applied, and the surplussolution pressed out, so as to forni between the filmcast and thecover-plate a thin film f, which serves to unite 'said film-.cast andcover-plate. (See Fig. 3.) The edges may then be cleaned off andsuitably bound in order to inish the replica readyfor use in thespectroscope.

By a Flying the mmlcast with its indeed face in ect contact with theplane glass the plane of the diiracting-'surface is preserved,

andthe ine scored lines, after drying, are` left as air-spaces betweenthe ilmand the glass, and by sealing the film-cast betweenV i two planeglass plates by the use of a cementing agent havlng approximately thesame refractive index as the lmlcast any optical deect due to irregularfilm-cast is eliminated and at the same time Vfthe cast is protected rmliability to injury.

:If the grating is'intended to be used by' transmitted li ht, aclear-glass plate c will be `used; btif t e grating, 1s to be employedwith reflected light a plate c, having a sllvered surface-such, forinstance, as represented at 'i in Fig. -wvill beemployed.

Havinor thus described my invention, I:

claim and desire to secure by Letters Patent- 1`.1 A diffraction-gratingreplica consisting .of a film-cast and a supporti r-plate upon whichsaid cast is mounted wit i the incised face of the cast 'next to theface of the plate.

2. A diffraction-grating replica consisting of a {ihn-cast, asupporting-plate against which the 'incised faceof the cast bears', a

ity in the thickness of the' cover-plate on the back of the cast, and a-securing agent therefor having substantially the same refractive indexas the film-cast.

3. A diiractionfgrating replica consisting of a ilm-cast,.and a silveredsupporting-phtte in contact with the incised face of the cast".

4. Aditractionating replica for spectroscopic work, Vsai replicaconsisting of a. film-cast with incised face composed 'ofribs whose topsare in a true plane. i

5.. A diffraction-grating 'replica for spectroscopic work, said repllcaconsisting ofxa` film-cast with incised face composed of rib's whosetops are in a true plane, and abackingplate with plane surface'against'whichthel back of the cast is cemented.

6. The combination of a diraction-.gr-ating replica 'with' platesbetween which said re lica is sealed.

n testimony whereof I have signed I'

